Microstructure evolution and properties of Mg-9Gd-0.8Al alloy with lamellar phase during extrusion at different temperatures

To clarify the evolution of lamellar phases in the initial microstructure of the Mg-9Gd-0.8Al alloy during the extrusion process and the effect of lamellar phases on the dynamic recrystallization of the extruded Mg alloy, the solid solution treated Mg-9Gd-0.8Al (SS10) alloy, was extruded at different temperatures (380, 400, and 450 °C). With the extrusion temperature increasing, the average size of dynamically recrystallized (DRXed) grains and the second phases decreases firstly and then increases. However, the volume fraction of DRXed grains shows an opposite trend, while the amount of the second phases consistently decreases. The as-extruded SS10 alloy demonstrates superior mechanical properties when extruded at 400 °C, with a yield strength (YS) of 240 MPa, ultimate tensile strength (UTS) of 298 MPa, and elongation (EL) of 19.3%. The alloy achieves enhanced strength through grain boundary strengthening, dislocation strengthening, and Orowan strengthening. Moreover, the presence of DRXed grains with a weak texture plays a significant role in the improvement of the ductility of the alloy.